Morphology: Enveloped, single-stranded negative-sense RNA virus. Family Orthomyxoviridae. Two lineages (Victoria, Yamagata — Yamagata not detected since 2020, may be extinct).
InfluenzaVirus
Typical drugs
- #1Oseltamivir— 75 mg PO BID × 5 days. Same dose as Flu A.
- #2Baloxavir Marboxil— Single-dose PO; equivalent.
Empiric therapy when resistant
Resistance to neuraminidase inhibitors uncommon in influenza B.
Resistance notes
Generally susceptible. Adamantanes never had activity against influenza B.
Pearls
Clinically managed identically to Flu A. Typically milder than Flu A but can be severe in children + young adults. Reye syndrome historically associated with flu B + aspirin in children — avoid ASA in children with viral infections. Annual vaccines now quadrivalent (covers both lineages historically; consideration to drop Yamagata given disappearance).
References
- IDSA Seasonal Influenza Guidelines (2018)